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TRANSCRIPT
News from fluctuation
and correlation analysis
from NA61/SHINE
at the CERN SPS
Maciej Rybczyński for the NA61/SHINE Collaboration
Jan Kochanowski University, Kielce
Fluctuations and correlations
1. May serve as a signature of the onset of deconfinement (OD) Close to the phase transition Equation of State changes rapidly which can impact energy dependence of fluctuations 2. Can help to locate the critical point of strongly interacting matter (CP) Analogy to critical opalescence – enlarged fluctuations close to the critical point. For strongly interacting matter maximum of CP signal expected when freeze-out happens near CP
http://www.msm.cam.ac.uk/doitpoms/tlplib/solid-solutions/videos/laser1.mov
NA61/SHINE detector layout
Unique, multi-purpose facility to study hadron production in hadron-proton, hadron-nucleus and nucleus-nucleus collisions at the CERN SPS
Large acceptance fixed target spectrometer exposed to primary (ions) and secondary (ions, hadrons) beams
Motivation of the NA61/SHINE
strong interaction programme
p+p and 7Be+9Be results to be shown in this presentation
Two-particle correlations in p+p - motivation
Two-particle correlations in Δη, Δϕ intervals.
Studied extensively at RHIC and LHC.
This method allows to disentangle different sources of correlations: - jets, - flow, - resonance decays, - quantum statistics effects, - conservation laws.
The motivation To study the sources of correlations at SPS, in the fixed target NA61 experiment.
Two-particle correlations in p+p - definitions
Correlations are calculated by finding the difference in pseudo-rapidity and azimuthal angle between two particles in the same event.
Δη=|η1 – η2| Δϕ=|ϕ1 –ϕ2|
The azimuthal angle is folded (to improve statistics): if Δϕ>π then Δϕ=2π-Δϕ .
Correlation function:
Correlation function ratio is calculated and normalized in restricted region: 0 < Δη < 3. Event and track cuts were chosen to select only inelastic interactions with particles produced in strong and EM processes within the NA61/SHINE acceptance. The results are corrected on detector effects: tracking inefficiencies, trigger bias.
Two-particle correlations in p+p - structures
Maximum at (Δη,Δϕ) = (0,π) - probably resonance decays and momentum conservation. - the strongest in unlike-sign pairs, - still visible in positively charged pairs (Δ++ decay), - non-visible in negatively charged (almost no double-negative resonances).
An enhancement at (0, 0) - probably Coulomb or quantum statistics effects. - not strong in unlike-sign pairs, - clearly visible in same charge pairs.
Two-particle correlations in p+p –
NA61 vs ALICE, energy dependence
M.Janik, PoS(WPCF2011) 026
Resonance decay hill is more visible at lower energies. Jets dominate at higher energies.
Two-particle correlations in p+p –
C(0,0) in NA61 and ALICE
C(0, 0) and C(0, π) in dependence of energy show monotonical behaviour. C(0, 0) rises with energy whereas C(0, π) decreases with energy.
Two-particle correlations in Δη, Δϕ
– a unique tool to test models NA61 EPOS 1.99 UrQMD 3.4
EPOS and UrQMD are with NA61 acceptance; all charged particles
Qualitative agreement of NA61 results with predictions of EPOS
Transverse momentum and multiplicity
fluctuations - motivation
(search for the Critical Point signal in fluctuations)
NA49 blazed a trail... NA49 Coll., Phys.Rev.C79 (2009) 044904; Phys.Rev.C70, (2004) 034902
NA61/SHINE goes further...
System-size scan with p, C, Si, and Pb beams at 158 GeV/c revealed an increase of fluctuations for medium-size systems, consistent with CP predictions
2D energy–system size scan is expected to give more insight into the CP location
Transverse momentum and multiplicity
fluctuations – measures
The most natural way to describe fluctuations of a quantity A is to use an intensive quantity, scaled variance:
However, in GCE, scaled variance can be expressed as:
thus depends on the the volume fluctuations via .
Measures independent of the unavoidable fluctuations from collision geometry must be used...
Transverse momentum and multiplicity
fluctuations – measures
Two families of strongly intensive quantities
where
independent of the volume and the volume fluctuations in GCE in the absence of fluctuations normalization factors chosen such, that
- both quantities are dimensionless - for the Independent Particle Model
Gorenstein, Gazdzicki, Phys. Rev. C 84 (2011) 014904 Gazdzicki, Gorenstein, Mackowiak-Pawlowska, Phys. Rev. C 88 (2013) 024907
For comparison with NA49
Transverse momentum and multiplicity
fluctuations – energy dependence
Transverse momentum and multiplicity
fluctuations – energy dependence
no structures which could be related to the CP in p+p, nor in Be+Be weak (if any) dependence of centrality in Be+Be Be+Be results close to p+p Bose-Einstein and/or PT/N − N anticorrelations
probably responsible for Δ and Σ difference
Transverse momentum and multiplicity
fluctuations – comparison with NA49
It is impossible to correct fluctuations for the acceptance, therefore to compare the ΦpT
results, NA49 cuts have been applied to the NA61/SHINE data. In NA49 because of high density of tracks, analysis was limited to forward rapidity region (1.1 < yπ < 2.6)
System size scan:
Both NA61/SHINE Be+Be and p+p consistent with the dependence suggested by NA49
Charge fluctuations of non-identified particles
New strongly intensive measures Δ and Σ (here applied to N+, N- fluctuations) → PR C88, 024907 (2013)
The analysis of Δ[NF ,NB] and Σ[NF ,NB] (left-right fluctuations) in NA61 is ongoing
Δ[N+, N-] and Σ[N+, N-] analysis 9 pseudorapidity intervals Can be sensitive to electric charge conservation effect and resonance decays.
N+ and N- fluctuations
in Be+Be collisions at 150A GeV/c
Δ[N+, N-] and Σ[N+, N-] almost independent of centrality
Both Δ[N+, N-] and Σ[N+, N-] smaller than 1 (possibly due to energy- momentum conservation and charge conservation effects)
Σ[N+, N-] decreases significantly with growth of
Tendency reproduced by EPOS (perfect agreement for Σ[N+, N-])
Systematic errors were estimated to be less than 5% for all points
Summary
Two-particle correlations in Δη, Δϕ intervals in inelastic p+p collisions were measured by the NA61/SHINE experiment. Models do not reproduce it.
Results on transverse momentum and multiplicity fluctuations for p+p and 7Be + 9Be were presented
No sign of the critical point
CP discovery waits for Ar+Sc, which will be presented soon...
Additonal slides
Physics program
1. Strong interactions program
a) search for the critical point of strongly interacting matter
b) study of the properties of the onset of deconfinement
c) study high pT particles production (energy dependence
of nuclear modification factor)
2. Hadron-production measurements for neutrino experiments
a) reference measurements of p+C interactions for the T2K experiment
for computing initial neutrino fluxes at J-PARC
3. Hadron-production measurements for cosmic ray experiments
a) reference measurements of p+C, p+p, p+C, and K+C interactions
for cosmic ray physics (Pierre-Auger and KASCADE experiments)
for improving air shower simulations
NA61/SHINE Detector
7Be+9Be@150A GeV/c
1. Large acceptance: 50%
2. High momentum resolution:
a) s(p)/p2 ≈ 10-4 (GeV /c)-1 (at full B=9 T m)
3. ToF walls resolution:
a) ToF-L/R: s(t) ≈ 60ps; ToF-F: s (t) ≈ 120ps
4. Good particle identification:
a) s(dE/dx)/ < dE/dx > ≈ 0.04; s(minv ) ≈ 5MeV
5. High detector efficiency: 95%
6. Event recording rate: 70 events/sec
Beams for NA61/SHINE
Beams at NA61/SHINE:
- Secondary
- Primary
Proton: 13, 20, 31, 40, 80, 158A GeV/c
Beryllium: 13, 20, 30, 40, 75, 150A GeV/c
Pion: 158, 350 GeV/c
Argon: 13, 20, 30, 40, 75, 150A GeV/c
Future beams:
- Xenon, Lead: 13, 20, 30, 40, 75, 150A GeV/c
Beam intensity at the NA61/SHINE detector up to 106 ions per 10 second spill
Secondary beryllium beam
Fragmentation target length optimized to maximize the production
of the desired fragment
Double magnetic spectrometer separates fragments according
to the selected magnetic rigidity
Possibility to use a degrader, Cu plate where ions lose energy according to the charge
Secondary beam
Centrality selection in ion collisions
PSD (Projectile Spectator Detector) is located on the beam axis and measures the forward energy EF related to the non-interacting nucleons of the beam nucleus
Cuts on EF allows to select different event classes
Four event classes
0 - 5% 5 - 10% 15 - 25% 10 - 15%
Two-particle correlations in p+p –
all charged pairs, energy dependence
The enhancement „saddle" at (0, 0) rises with increasing beam momentum.
Two-particle correlations in p+p –
unlike-sign pairs, energy dependence
The enhancement at (0, 0) rises, like in previous slide, with increasing beam momentum.